CASCADE REFRIGERATION SYSTEM WITH MODULAR AMMONIA CHILLER UNITS

• US 20120117996A1
• Filed: 11/17/2010
• Published: 05/17/2012
• Est. Priority Date: 11/17/2010
• Status: Active Grant

• Current Assignee: Hill Phoenix Incorporated (Dover Corporation)
• Original Assignee: Hill Phoenix Incorporated (Dover Corporation)
• Inventors: Hinde, David K., Bittner, John D., Zha, Shitong, Poland, Joseph R.
• Granted Patent: US 9,541,311 B2
• Time in Patent Office: Days
• US Class Current: 62/192
• CPC Class Codes: F25B 2400/06 Several compression cycles arranged in parallel
• CPC Class Codes: F25B 2600/21 Refrigerant outlet evaporator temperature
• CPC Class Codes: F25B 7/00 Compression machines, plants or systems, with cascade operation, i.e. with two or more circuits, the heat from the condenser of one circuit being absorbed by the evaporator of the next circuit F25B9/00 takes precedence
• CPC Class Codes: F25B 9/002 characterised by the refrigerant

Abstract

A cascade refrigeration system includes an upper portion having at least one modular chiller unit that provides cooling to at least one of a low temperature subsystem having a plurality of low temperature loads, and a medium temperature subsystem having a plurality of medium temperature loads. The modular chiller unit includes a refrigerant circuit having at least a compressor, a condenser, an expansion device, and an evaporator. An ammonia refrigerant mixed with a soluble oil circulates within the refrigerant circuit. A control device may be programmed to modulate the position of the expansion device so that a superheat temperature of the ammonia refrigerant near an outlet of the evaporator fluctuates within a substantially predetermined superheat temperature range to positively return soluble oil from the evaporator to the compressor.

Claims

1. A cascade refrigeration system, comprising:

an upper portion having at least one modular chiller unit that provides cooling to at least one of a low temperature subsystem having a plurality of low temperature loads, and a medium temperature subsystem having a plurality of medium temperature loads;

the modular chiller unit comprising;

a refrigerant circuit having at least a compressor, a condenser, an expansion device, and an evaporator; and

an ammonia refrigerant configured for circulation within the refrigerant circuit; and

an ammonia refrigerant accumulator configured to receive the ammonia refrigerant from the evaporator.

2. The cascade refrigeration system of claim 1 further comprising both the low temperature subsystem and the medium temperature subsystem, and wherein the low temperature subsystem comprises a CO2 refrigerant, and the medium temperature subsystem comprises a chilled liquid coolant comprising at least one of water and glycol, so that the cascade refrigeration system comprises only naturally-occurring refrigerants and environmentally safe coolants and is substantially HFC-free.

3. The cascade refrigeration system of claim 1 further comprising both the low temperature subsystem and the medium temperature subsystem, and wherein the low temperature subsystem comprises a CO2 refrigerant, and the medium temperature subsystem comprises a CO2 liquid coolant, so that the cascade refrigeration system comprises only naturally-occurring refrigerants and coolants and is substantially HFC-free.

4. The cascade refrigeration system of claim 1 further comprising a soluble oil mixed with the ammonia refrigerant, and wherein the ammonia refrigerant accumulator is configured to receive the soluble oil flushed from the evaporator and return the flushed soluble oil to the compressor.

5. The cascade refrigeration system of claim 1 wherein the soluble oil comprises a PolyAlkylene Glycol (PAG) oil.

6. The cascade refrigeration system of claim 1 wherein the modular chiller unit contains a critical charge amount of the ammonia refrigerant and operates without an ammonia receiver tank.

7. The cascade refrigeration system of claim 6 wherein the critical charge amount of the ammonia refrigerant is less than approximately 20 pounds.

8. The cascade refrigeration system of claim 1 further comprising a control device programmed to modulate the position of the expansion device so that a superheat temperature of the ammonia refrigerant proximate an outlet of the evaporator fluctuates within a substantially predetermined superheat temperature range.

9. The cascade refrigeration system of claim 8 wherein the predetermined superheat temperature range is within the range of approximately 0-10 degrees F.

10. The cascade refrigeration system of claim 8 wherein the control device is programmed to be over-reactive in order to modulate the position of the expansion device so that the superheat temperature of the ammonia refrigerant proximate an outlet of the evaporator fluctuates within the substantially predetermined superheat temperature range.

11. The cascade refrigeration system of claim 1 wherein the modular chiller unit comprises a plurality of modular chiller units arranged in a parallel configuration and packaged within a transportable enclosure configured for shipping and direct installation at a facility.

12. The cascade refrigeration system of claim 1 wherein the evaporator and condenser comprise plate heat exchangers formed at least partially from stainless steel.

13. The cascade refrigeration system of claim 1 wherein the condenser of the modular chiller unit comprises a water-cooled condenser that interfaces with a water coolant loop having one or more heat reclaim devices.

14. The cascade refrigeration system of claim 1 wherein the condenser of the modular chiller unit comprises an air-cooled microchannel condenser.

15. The cascade refrigeration system of claim 14 wherein the air-cooled microchannel condenser includes evaporative cooling.

16. The cascade refrigeration system of claim 1 wherein the modular chiller unit further comprises one or more heat reclaim devices configured to de-superheat hot gas ammonia refrigerant discharged from the compressor prior to being received by the condenser.

22. The modular ammonia chiller unit of claim 16 further comprising an ammonia refrigerant accumulator configured to receive the accumulation of the soluble oil from the evaporator for return to the compressor.

17. A modular ammonia chiller unit for a refrigeration system, comprising:

a refrigerant circuit having at least a compressor, a condenser, an expansion device, and an evaporator;

an ammonia refrigerant; and

a soluble oil mixed with the ammonia refrigerant.

18. The modular ammonia chiller unit of claim 17 further comprising a control device operated according to a control scheme configured to at least partially remove an accumulation of the soluble oil from the evaporator.

19. The modular ammonia chiller unit of claim 18 wherein the control scheme comprises programming the control device to over-reactively modulate the position of the expansion device so that a superheat temperature of the ammonia refrigerant proximate an outlet of the evaporator fluctuates within a superheat temperature range.

20. The modular ammonia chiller unit of claim 18 wherein the control scheme comprises periodically stopping and restarting the chiller unit.

21. The modular ammonia chiller unit of claim 18 wherein the control scheme comprises returning the accumulation of the soluble oil from the evaporator through a siphon line to a location in the refrigerant circuit upstream of the expansion device.

23. A method of providing a cascade refrigeration system that is substantially HFC-free, comprising:

providing a lower portion having at least one of a low temperature subsystem that uses carbon dioxide as a refrigerant to cool a plurality of low temperature loads, and a medium temperature subsystem that uses one of CO2 and a water-glycol mixture as a liquid coolant to cool a plurality of medium temperature loads;

providing an upper portion having at least one modular chiller unit that provides cooling to the low temperature subsystem and the medium temperature subsystem, the modular chiller unit comprising a refrigerant circuit having at least a compressor, a condenser, an expansion device, and an evaporator;

charging the refrigerant circuit of the modular chiller unit with a critical charge amount of an ammonia refrigerant; and

programming a control device to operate according to a control scheme that modulates a superheat temperature of the ammonia refrigerant.

24. The method of claim 23 further comprising the step of mixing a soluble oil with the ammonia refrigerant, and wherein the step of programming a control device to operate according to a control scheme is configured to at least partially remove an accumulation of the soluble oil from the evaporator.

25. The method of claim 24 wherein the control scheme comprises modulating the position of the expansion device so that a superheat temperature of the ammonia refrigerant proximate an outlet of the evaporator fluctuates within a superheat temperature range of approximately 0-10 degrees F.

26. The method of claim 24 wherein the control scheme comprises periodically stopping and restarting the chiller unit.

27. The method of claim 24 wherein the control scheme comprises returning the accumulation of the soluble oil from the evaporator through a siphon line to a location in the refrigerant circuit upstream of the expansion device.

28. The method of claim 23 further comprising providing an ammonia refrigerant accumulator configured to receive the accumulation of the soluble oil from the evaporator for return to the compressor.